1. Field of the Invention
The present invention relates to an addressing method for a memory unit, and more particularly to an addressing method capable of increasing addresses with an increased memory capacity.
2. Description of the Prior Arts
Computer systems have been employed wherein a memory which stores specified programs and data is detachably provided to a machine main body as a memory unit so as to cope with various applications. For example, in a character image generating circuit of a laser printer, a font ROM for converting character data sent from a host computer into images is constructed as memory; unit (font cartridge) for every style or size of characters so as it to be capable of mounting to the machine main body if need be. However, the memory capacity of the memory unit has markedly increased with the high demand for such a system and remarkable progress of semiconductive memory technology. As a result, the number of available bits has increased for designating an address of the memory, frequently causing deficiency in the number of signal lines between the machine main body and the memory unit. However, simply providing an increased number of signal lines will only give rise to an increased number of connectors, entailing a problem in that there is no replaceability between machines of conventional type and those of a new type.